Miniature actuator integration for liquid cooling

ABSTRACT

A device for cooling integrated circuits on circuit boards. A base placed proximate the element to be cooled contains an actuator that forces a cooling liquid through a plurality of channels that dissipate heat generated by the element. The base with the actuator, liquid and channels is sealed with a top. Preferred actuators are electric motors, and MEMS such as electrostatic actuators and piezoelectric actuators. The base has a large surface area relative to the thickness of the chamber The ratio of the surface area to thickness may range from about 40:1 to about 5:1.

FIELD OF THE INVENTION

The present invention relates in general to liquid cooling of integratedcircuits and, more particularly, to low cost miniature actuatorsincorporated directly into the heat spreader or sink.

BACKGROUND OF THE INVENTION

Liquid cooling is known to have a significantly better heat transfercapability than solid conduction cooling. However, a low cost method ofrecirculating liquids through a hot region of an integrated circuit (IC)has yet to be successfully accomplished. Also, in CPUs, it is possibleto use fans and blowers to move air across those components thatgenerate heat, but it is also not as efficient as liquid heat transfermethods.

The current method for regular desktop CPU cooling is a passivecomponent of air cooled thermal solutions. Located above a silicon chipon a IC board is a heat spreader, such as a flat conductive sheet of,for example, copper or other conductive materials. Above the flatconductive sheet is a heat sink, which comprises a flat surfaceinterfacing the flat conductive sheet and a plurality of outwardlyextending elements that contain a heat transfer thermal solution that isair cooled by air passing through and adjacent to the outwardlyextending elements.

It has been proposed to cool ICs using an external pump. However, thesepumps are quite expensive compared to the cost of the IC, and do notalways seal effectively. None have demonstrated an expectation to meetan IC life requirement of 3 to 7 years or more.

One of the major costs in using external pump is liquid sealing, toprevent leaks and isolate the pump actuator from the liquid. Inaddition, some cooling systems have volume constraints, which make largepumps unfeasible. Moreover, small liquid pumps cannot meet the liferequirements of most, if not all, IC designs.

At the present time there is a need for a way to cool ICs and othersmall sources of a lot of heat. It would be of great advantage if aliquid cooling system could be developed for most, if not all, ICdesigns.

Another advantage would be if the cooling system would be low in costand high in reliability, especially over the life expectancy of the ICdesign.

Yet another advantage would be if a cooling system could be developedthat would eliminate sealing concerns while having the appropriatecapacity for the IC design.

Other advantages and features will appear hereinafter.

SUMMARY OF THE INVENTION

The present invention provides a low cost, effective liquid coolingdevice for cooling IC elements that generate heat when used. In itssimplest form the invention includes a base that is to be placedproximate the element to be cooled that defines a chamber. Inside thechamber is an actuator that forces a cooling fluid, preferably a liquidsuch as water, through a plurality of channels or loops that dissipateheat generated by the element such as an IC chip. The base with theactuator, liquid and channels is sealed with a top.

Preferred actuators are electric motors, Micro-Electro-MechanicalSystems (MEMS) such as electrostatic actuators and piezoelectricactuators. The base has a large surface area relative to the thicknessof the chamber The ratio of the surface area to thickness may range fromabout 40:1 to about 5:1.

It is understood that the device is constructed of conductive materialsand that the actuator is capable of operating in the fluid being forcedthrough the microchannels.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the invention, reference is herebymade to the drawings, in which:

FIG. 1 is a side elevational view, in section, of one embodiment of thepresent invention;

FIG. 2 is a section view taken along the line 2-2 of FIG. 1;

FIG. 3 is a section view taken along the line 3-3 of FIG. 1;

FIG. 4 is a plan view of the top used with the device of FIG. 1; and

FIG. 5 is a section view taken along the line of FIG. 4.

In the figures, like reference characters designate identical orcorresponding components and units throughout the several views.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to the figures, the device 10 generally includes a base 11,which is formed from a thermally conductive material such as copper orother thermally conductive materials used in the integrated circuitindustry. Base 11 has a relatively large surface area. In one embodimentthe length 13 and width 15 are about 50 mm each, while the sides 17 areabout 7 mm, thus defining a chamber. This gives a ratio of surface areato thickness of about 50:7, or roughly 7:1. Preferred ratios may rangefrom about 40:1 to about 5:1. The essential requirement is that thesurface area is sufficient to dissipate all the heat from the elementalong its bottom. One advantage of this method is that the liquid flowinside can effectively carry and spread heat to large surface areasquite uniformly.

Inside the chamber defined by base 11 and sides 17 is a cooling fluid19. Fluid 19 is preferably a liquid, and most preferably water. It maybe appropriate to use distilled or deionized water to prevent internalreaction between the material of the base 111 and sides 17, as well asother components. Also inside the chamber is a micro channel plate 21,which includes a plurality of channels or loops 23 that define a pathfor the fluid 19 to flow, to present the fluid to a cooling surface area25. Motor 27 is used to force the fluid 19 into and through theplurality of channels 23 in micro channel plate 21. Of course top 29covers the device to form a sealed chamber that is not affected by anyexternal contact. Top 29 may also be made of copper or other conductivematerials and in a preferred embodiment is made of the same material asbase 11 and sides 17.

In the figures, the actuator of this invention is shown as a motor. Anyactuator that can apply pressure to a fluid and force it to pass throughthe micro channels is appropriate for this invention. Other actuatorsinclude, but are not limited to, electrostatic actuators andpiezoelectric actuators that are commercially available. All that isrequired is that the actuator, whether a motor or other device, have thepower to force the liquid through the micro channels and operate overthe expected life of the device, which should be at least three to sevenyears and preferably up to ten years or more.

One advantage of the present invention is that with the actuator, suchas motor 27, sealed with the liquid together inside the chamber, thedevice does not have liquid sealing issues that occur when externalpumps are used. Thus the device has a substantially improved actuatingreliability.

The present invention also demonstrates a strong lateral heat spreadingcapability that makes it admirably suitable for removing heat from asmall area, such as an IC chip. The device spreads the heat to a largearea, as shown, or carries the heat in the liquid to an external heatsink or heat exchanger. It is also possible to transfer theheat-containing liquid through an outlet to a liquid-air heat exchangeror other heat sink that may or may not be cooled by a fan or blower. Ineffect the present invention provides a number of ways to dissipate theheat generated by an element, such as but not limited to IC elements. Itmay operate to transmit the heat containing fluid in the micro channels23 in contact with the top 29, which in turn dissipates heat outward andaway from the element being cooled. Alternatively the liquid may betransmitted while still inside a sealed structure without external pipesor channels. The liquid can thus be sent to a heat sink as noted herein,with or without the fan or blower, and it can be sent through additionalmicro channels or other channels, not shown, to allow the liquid to becooled before returning it to the chamber.

While particular embodiments of the present invention have beenillustrated and described, they are merely exemplary and a personskilled in the art may make variations and modifications to theembodiments described herein without departing from the spirit and scopeof the present invention. All such equivalent variations andmodifications are intended to be included within the scope of thisinvention, and it is not intended to limit the invention, except asdefined by the following claims.

1. A device for cooling elements that generate heat, comprising: a basefor defining a chamber, said base being adapted to be placed proximatethe element to be cooled; a coolant fluid in said chamber; a micro/minichannel element in said chamber for directing flow of said coolant fluidthrough a plurality of channels or loops; a miniature actuatorintegrated in said chamber for forcing said cooling fluid through saidplurality of channels in said micro/mini channel element having asurface area to thereby dissipate heat generated by said element; and atop for sealing said chamber and maintaining said coolant fluid insidesaid base.
 2. The device of claim 1, wherein said coolant fluid is aliquid.
 3. The device of claim 2, wherein said liquid is water.
 4. Thedevice of claim 1, wherein said base is thermally conductive metal. 5.The device of claim 1, wherein said actuator is an electric motor foroperating in said fluid.
 6. The device of claim 1, wherein said actuatoris an electrostatic actuator.
 7. The device of claim 1, wherein saidactuator is a piezoelectric actuator.
 8. The device of claim 1, whereinsaid element to be cooled is an integrated circuit chip.
 9. The deviceof claim 1, wherein said base has a large surface area relative to thethickness of said chamber.
 10. The device of claim 9, wherein the ratioof said surface area to thickness ranges from about 40:1 to about 5:1.11. A device for cooling elements that generate heat, comprising: basemeans for defining a chamber, said base means being adapted to be placedproximate the element to be cooled; a coolant fluid in said chamber;micro/mini channel element means in said chamber for directing flow ofsaid coolant fluid through a plurality of channels in said micro channelelement means; miniature actuator means integrated in said chamber forforcing said cooling fluid through said plurality of channels in saidmicro/mini channel element means having a surface area to therebydissipate heat generated by said element; and top means for sealing saidchamber and maintaining said coolant fluid inside said base means. 12.The device of claim 11, wherein said coolant fluid is a liquid.
 13. Thedevice of claim 12, wherein said liquid is water.
 14. The device ofclaim 11, wherein said base means is formed from thermally conductivemetal.
 15. The device of claim 11, wherein said actuator means is anelectric motor for operating in said fluid.
 16. The device of claim 11,wherein said actuator means is an electrostatic actuator.
 17. The deviceof claim 11, wherein said actuator means is a piezoelectric actuator.18. The device of claim 11, wherein said element to be cooled is anintegrated circuit chip.
 19. The device of claim 11, wherein said basemeans has a large surface area relative to the thickness of saidchamber.
 20. The device of claim 19, wherein the ratio of said surfacearea to thickness ranges from about 40:1 to about 5:1.